Question

已知X二次方-3X+1=0.求X二次方+X二次方分之1的值

Answer 1

x^2-3x+1=0

x^2+1=3x 两边除x

x+1/x=3 平方

x^2+2+1/x^2=9

x^2+1/x^2=9-2=7